The present invention relates to a pneumatic tire, more particularly to a bias ply tire with an improved inner tread structure which is suitable for racing karts.
Karting is one of the fastest growing forms of motor sport in the world. In recent years, the maximum running speed reaches over 100 kilometer/hr and the running distance in a race becomes increased. The kart tires, which have a low aspect ratio of not more than 0.5 and a very small diameter of not more than 300 mm, are required to have not only excellent high-speed performance such as maneuverability (grip), acceleration (traction) and the like but also long life being capable of maintaining the excellent performance in order to shorten lap time.
It is therefore, an object of the present invention to provide a bias tire, in which maneuverability, acceleration and the like are improved and endure long time in spite of high-hysteresis soft tread rubber compound, and thereby being possible to shorten lap time.
According to the present invention, a bias tire comprises a tread portion, a pair of sidewall portions, a pair of bead portions each with a bead core therein, a carcass extending between the bead portions and comprising two cross plies of cords, and a tread rubber disposed radially outside a crown portion of the carcass to define a tread face, wherein the loss tangent of the tread rubber is in a range of 0.40 to 0.60 under a temperature of 50 deg.C., the distance between the tread rubber and the adjacent cords of the radially outermost carcass ply is at most 1.0 mm, and the above-mentioned two cross plies include at least one ply of PEN cords made of polyethylene 2,6 naphthalate fibers twisted together.